The use of expandable tubulars is becoming more common in the drilling and completion phases of well bore construction. U.S. Pat. No. 6,098,717 (BAILEY et al) discloses such an expandable tubular and also an expandable spacer.
Several designs of expandable centraliser have been described for use with expandable tubulars.
U.S. Pat. No. 5,358,040 (KINLEY et al) discloses a centraliser with mechanical roller arms which are limited in terms of extension. This centraliser is mechanically relatively complex, and liable to failure
WO 03/006789 A1 (SHELL) discloses an expandable wellbore stabliser. Therein pre-energised arms are released upon expansion of a radially expandable tubular element, the arms thereafter being retained in place by action of a spring force. Although this stabliser is relatively simple, it suffers from a number of problems, e.g. if the arms are released prematurely the centraliser may become stuck downhole at an undesirable location.
WO 03/078789 A1 (DOWNHOLE PRODUCTS) discloses a slotted expandable centraliser adapted for use with slotted expandable casing.
The content of the prior art documents mentioned hereinbefore is incorporated herein by reference.
It is an object of at least one embodiment of at least one aspect of the present invention to obviate or mitigate one or more problems in the prior art.
It is also an object of at least one embodiment of at least one aspect of the present invention to provide an improved expandable centraliser which may be adjustable.
It is a further object of at least one embodiment of at least one aspect of the present invention to provide an improved expandable centraliser which instead of seeking to mitigate against tension, seeks to benefit from compression.
A concept behind at least one aspect of the present invention is as follows. Previous art has essentially attempted to mitigate the effect of the pipe expansion, i.e. using tension caused in the centraliser body. The centraliser of the invention uses the expansion of the tubing to cause compressive forces, which are exerted over known distances to energise blades of the centraliser by using relative motion caused by said expansion.